This invention relates to a signaling system for use in a connection-oriented packet network.
In a connection-oriented packet network known in the art, connection and disconnection between endpoints or terminals are carried out by the use of a control protocol which is generally called a signaling procedure in the art. A conventional signaling procedure has been created on the supposition that simple-functional terminals such as telephone sets are accommodated in the packet network. In the conventional signaling procedure, a number of messages must be exchanged. As a result, an operation of each of the connection and the disconnection is complicated and will hereunder be called a signaling operation. It is therefore difficult to establish the connection at a high speed. If the conventional signaling procedure is straightforwardly used in a high-performance network accommodating connectionless terminals such as computers, a connection delay becomes a serious problem for those software programs in which a response is required.
The above-mentioned control protocol is described in the CCITT recommendation "Draft Text for Q.93B" (pages 1 to 72) prepared in the Working Party XI/6 of the CCITT Study Group XI held in Geneva on Jun. 22 to 26, 1992.
In the CCITT recommendation Q.93B, a signaling operation is carried out by exchanging a series of messages. Specifically, those messages comprise six connection-establishing messages including a setup message, three connection-releasing messages including a disconnect message, and three other messages including a status message. Each message is composed of a common portion and a specific portion inherent to the message. The common portion comprises a protocol identifier, a call number, a message type, and so on. In order to establish connection, the above-mentioned connection-establishing messages are exchanged so that the terminals acquire a transmission virtual channel (VC) and an end-to-end communication route. Accordingly, even if the amount of transmission data is small, a processing delay and a propagation delay are not ignorable.
In order to perform the signaling operation at a high speed, it is necessary to minimize the processing delay in each switch which is included in the connection-oriented packet network in the manner known in the art. The processing delay is mainly caused by selection of the communication route. Therefore, it is desired to perform such selection at a high speed.
In the CCITT recommendation Q.93B, the setup message for establishment of connection contains a called party number and a called party subaddress in an information element so as to designate a called party to be connected. Supplied with the setup message, each switch decides a next route with reference to the called party number contained in the setup message. After the setup message reaches the called party address terminal, the signaling operation is carried out again by the use of the called party subaddress. Thus, selection of the route is carried out by the hop-by-hop signaling operation. When the multi-stage switches are passed, the processing time for selection of the route at each switch is increased and the end-to-end VC setup time is increased.